In recent years, a hybrid vehicle, an electric vehicle, and the like with environmental consideration have been developed, and these vehicles include a motor as a driving source. Of these vehicles, there is a vehicle which includes a plurality of motors (including motor generators or generators). An AC motor is used as the motor, DC power is converted to three-phase AC power by an inverter, and the motor is driven with three-phase AC power. Since a high voltage is needed so as to output high rotation or high torque with the motor, a DC voltage of a battery is boosted to a DC high voltage by a voltage boost converter, and the DC high voltage is supplied to the inverter. For this reason, in a vehicle, in order to control the motor, inverter control for controlling switching of a switching element of the inverter and voltage boost control for controlling switching of a switching element of the voltage boost converter are performed. A smoothing capacitor is provided between the voltage boost converter and the inverter, and a voltage (a DC high voltage after boosting by the voltage boost converter) across both ends of the smoothing capacitor is detected by a voltage sensor. In the voltage boost control, control is performed such that a target voltage necessary for driving the motor is reached using the DC high voltage detected by the voltage sensor. In particular, in a case of a system which includes a plurality of motors, a target voltage necessary for driving each motor is set, and a target voltage of the system is selected from among the plurality of target voltages.
Patent Literature 1 describes a control device for a vehicle which includes two motor generators. In this control device, a gate signal for controlling a switching element of a voltage boost converter is generated on the basis of a sensor value of a voltage of a DC power supply, a sensor value of a voltage across both ends of a smoothing capacitor, a motor torque command value of each motor generator, and a motor rotation speed, and a gate signal for controlling a switching element of an inverter is generated on the basis of a sensor value across both ends of the smoothing capacitor, a motor torque command value, and a sensor value of a motor current for each motor generator.